I. Field of the Invention
This disclosure relates generally to systems, apparatus and methods for wireless position estimation, and more particularly, to indoor ranging based on an auto-correlation of a subset of OFDM subcarriers.
II. Background
A mobile device may use GPS to find its current position and provide a good fix. In doors, however, GPS signals are blocked and good GPS fixes are unreliable or impossible. The mobile device may switch to internal sensors (e.g., from accelerometers, gyrometers and magnetometers) determine how far and in which direction the mobile device travelled from the last good fix. Alternatively, the mobile device may record RSSI and/or RTT measurements from nearby wireless access points (APs). The RSSI measurements may be used for ranging; however, the resulting ranges have a high degree of uncertainty of 50 to 100 feet. The RTT measurements provide a lower degree of uncertainty; however, the uncertainty may still be 10 to 50 feet. By estimating ranges to three or more APs, the mobile device may use trilateration to estimate its location but the degree of uncertainty remains.
What is needed is a way to determine a mobile device's range and position to a higher degree of accuracy.